Hops are an essential ingredient in the brewing industry. Hops, or the extracts thereof such as certain acids and oils, give to beer and ale such qualities as their distinctive bitter taste, mouthfeel, cling, aroma and foamability.
Traditionally, the entire hop was added to and boiled with the wort which resulted in the leaching of the hop constituents into the wort. More recently however, hops have been processed independently to extract the desired constituents, and these constituents are then added at some point in the brewing process. The independent extraction, processing, and addition of the hop components provides greater control over the brewing process.
Alpha acids, also referred to as humulones, are one of the above-mentioned extracts from hops. After extraction from the hops, the alpha acids are isomerized into isoalpha acids (isohumulones) by exposing them to high temperatures and basic conditions. Isoalpha acids contribute to the bitterness of beer. Beta acids, also referred to as lupulones, are another extract from hops. Beta acids can be converted into isoalpha acids through a series of steps including hydrogenation, oxidation, heating, and raising the pH (see U.S. Pat. No. 4,644,084 to Cowles and U.S. Pat. No. 4,918,240 to Todd et al.).
One problem well known in the brewing industry is that isoalpha acids are susceptible to degradation upon exposure to light. This degradation produces a highly undesirable skunk-like odor in the beer. It is also well known in the art that hydrogenating the isoalpha acids (or the precursor alpha or beta acids) will increase the light stability of the beer. This hydrogenation requires catalysis, such catalysis usually employing a palladium on carbon catalyst.
During the hydrogenation of alpha, beta, or isoalpha acids however, compounds which are referred to as catalyst poisons, and which are associated with the hop extract, foul the catalyst. This fouling of the catalyst causes the hydrogenation of the alpha, beta, or isoalpha acids to proceed slower than normal and eventually to cease before all of the alpha, beta, or isoalpha acids are hydrogenated. In some instances, the catalyst becomes so quickly fouled that it must be replaced during the middle of the hydrogenation process in order for the hydrogenation to proceed to completion. However, simple replacement or changeout of the catalyst is an unsuitable solution to the poisoning problem for at least two reasons. First, the substitution of a new catalyst midway through the hydrogenation process can promote the formation of overreaction products. Second, the catalyst is quite expensive, and frequent replacement of the catalyst greatly adds to the cost of production.
Consequently, an object of the present invention is to remove catalyst poisons from components of hop extracts prior to the hydrogenation of such components thereby preventing the fouling of hydrogenation catalysts and allowing the hydrogenation to proceed to completion.
Another object of the invention is to provide a hydrogenation process for components of hop extracts that will not contribute to the formation of overreaction products.
A further object of the invention is to extend the life of the hydrogenation catalyst thereby preventing the frequent changeout of the expensive catalyst.